NAME

       GFA - output primitive for filling polygonal areas.

SYNOPSIS

       CALL GFA (N, X, Y)

C-BINDING SYNOPSIS

       #include <ncarg/gks.h>

       void gfill_area(const Gpoint_list *point_list);

DESCRIPTION

       N           (Integer,  Input)  - The number of points in the polygon to be filled.  N must
                   be greater than two.

       X (N)       (Real Array, Integer) - The X world coordinates of the polygon.

       Y (N)       (Real Array, Integer) - The Y world coordinates of the polygon.

USAGE

       The area to be filled is delimited by the sequence of straight  line  segments  connecting
       the  successive  points   (X(1), Y(1)), (X(2), Y(2)), ..., (X(N), Y(N)). The last point in
       the polygon is connected to the first point with a straight line segment in the case  that
       (X(N), Y(N)) does not equal (X(l), Y(l)).

       Given  a polygon whose edges cross each other, it becomes ambiguous as to what constitutes
       the "inside" of the polygon.  The algorithm used in GKS is as follows: for a given  point,
       draw a ray starting at that point and going to infinity in any direction; if the number of
       intersections between the ray and the polygon is odd, the point  is  within  the  polygon,
       otherwise  it  is  outside.   If  the  straight  line  passes  through  a  polygon  vertex
       tangentially, the intersection count is not affected.  If a point is within  the  polygon,
       it is included in the area to be filled.

       Several  interior styles (hollow, solid, and various hatch patterns) can be selected.  See
       the man pages for gsfais and gsfasi for these.

       Note well: By default in GKS, the interior fill style is hollow, or no fill. If  you  call
       GFA  and  do  not  get  a  filled interior as you expected, you will probably need to call
       GSFAIS to set the fill style to something other than "hollow".

ACCESS

       To use GKS routines, load the NCAR GKS-0A library ncarg_gks.

SEE ALSO

       Online: gsfais, gsfasi, gscr, gsfaci, gqfais, gqfasi, gfill_area

       Hardcopy: User's Guide for NCAR GKS-0A Graphics; NCAR Graphics Fundamentals, UNIX Version

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.